Cell migration in 3D tissue space is of fundamental importance for human biology. However, predicting and programming 3D cell motility remain as major challenges despite of a firm picture of the molecular machineries involved. To fill the knowledge gap between the overwhelming subcellular details such as protein-protein interactions, and the fascinating dynamic patterns exhibited by different cell types in tissue spaces, I will focus on the mesoscale cellular dynamics, namely the migration mode transitions of cells in 3D extracellular matrix (ECM). My lab has developed deep-learning based image postprocessing to track the migration modes of cells. We also developed techniques to manipulate and measure the micromechanics of ECM at cellular scale. Based on these preliminary results, I will systematically study the intrinsic and extrinsic control mechanisms of 3D cell migration mode transitions in collagen ECM. The results will pave the way for my long-term goals to understand the organizing principle that lead molecules to life, and to program cell motility for applications in tissue engineering and cancer treatment. To this end, I will dedicate my lab to the following research thrusts. Thrust 1 aims to determine how cell migration mode transitions are regulated by external cues, as well as intrinsic states of cells during the Epithelial-Mesenchymal Transition (EMT). I will test three hypotheses that elucidate the roles of ECM micromechanical stiffness, anisotropy, plasticity, synergy of mechanical and chemical guidance, as well as EMT stage in modulating the cell migration mode transitions. I will employ sophisticated ECM engineering and characterization techniques developed in my lab. I will also use genetically engineered cells whose EMT transcription factors are fluorescent labeled and can be specifically activated. Completion of thrust 1 will establish 3D cell migration as a hidden Markov process where the mesoscale dynamics, namely the migration mode transitions, provides a unifying framework to explain diverse dynamic patterns of 3D cell migration observed in vivo. Thrust 2 aims to devise strategies to program cell migration via nonstationary mechanical cues. In subproject 1, I will employ techniques developed in my lab to control 3D contact guidance cues in space and in real time. By measuring the migration mode transitions under step-increasing contact guidance, I will obtain the energy barriers that separate different modes. Then under periodic mechanical stimuli I will measure and computationally model the nonequilibrium mode transition flux, a statistical physics quantity that inform the efficiency and energy dissipation of cell motility responses. These mesoscale quantities shed light to the underlying molecular organizing principles. In subproject 2 I will develop collagen ECM which exhibits digital response to stresses using DNA-grafted nanoparticles as crosslinkers. I will design the DNA sequence to control the yield strength of crosslinkers, thereby programing cell migration mode both for single cell and for collective organoid migration. Completion of thrust 2 will expands the design space of engineered ECM, laying a foundation for the mechanical programing of 3D cell motility.